The disclosed embodiments of the present invention relate to a signal generation apparatus, and more particularly, to a signal generation apparatus capable of outputting a high-linearity class AB signal.
A transmitter with class AB operation is a good candidate for high power efficiency design. A current mode transmitter has the merit of high speed operation compared to its voltage mode counterpart. To achieve the class AB operation in a conventional current mode transmitter, both sink and source driving devices are needed in a class AB current driver. An output current of the class AB current driver is the superposition of a source current and a sink current, which correspond to a p-channel metal-oxide-semiconductor field-effect transistor (PMOS) digital-to-analog converter (DAC) and an n-channel metal-oxide-semiconductor field-effect transistor (NMOS) DAC, respectively. Due to the timing skew and gain error between the sink current and the source current, the linearity of the output current is reduced in the class AB current driver.
In a higher operating frequency, the device/timing mismatches will degrade the linearity of the output current more severely. Thus, there is a need for a novel current generation scheme to generate a high-linearity class AB output current.